Electronic mails (e-mails) are continually transmitted and received via a network such as the Internet. With an increased frequency of making business communications and notifications via the e-mails, a quantity of the e-mails received by the individuals rises at a dramatic rate. While on the other hand, some of the communications and the notifications via the e-mails request a reply to the received communication or notification within a designated time-limit. Under such circumstances, a recipient of the e-mail might misapprehend a designated reply time-limit. Further, the e-mail requested to reply might be intermingled with other e-mails, resulting in failing to reply within the designated reply time-limit.
Over the recent years, there has been known a technique of attaching, to the e-mail, a flag for knowing the recipient that a sender is important or special in order to assist management of the e-mails.                [Patent document 1] Japanese Laid-Open Patent Publication No. 07-162452        [Patent document 2] Japanese Laid-Open Patent Publication No. 2009-135855        [Patent document 3] Japanese Laid-Open Patent Publication No. 07-183912        [Patent document 4] Japanese Laid-Open Patent Publication No. 10-136010        